1. Field of the Invention
The present invention relates to turbo machines, and in particular relates to a turbo machine being able to prevent from instability in flow, by suppressing swirl due to recirculation flow at an inlet of an impeller and by suppressing rotation stalls of the impeller, irrespective of the types and the fluid thereof.
In more details, the present invention relates to the turbo machines, such as for a pump, a compressor, a blower, etc., having non-volume type impeller therein, and in particular, relates to the turbo machine being able to prevent from the instability in flow, by suppressing a swirl or pre-whirl which is generated due to a main flow or component of the recirculation occurring at an inlet of an impeller and by suppressing rotation stalls thereof, thereby being suitable to be applied into a mixed-flow pump, which is used widely as water circulating pumps in a thermal power plant or in a nuclear power plant, or as drainage pumps, etc.
2. Description of Prior Art
Rotary machines being called by a name of xe2x80x9cturbo machinexe2x80x9d can be classified as below, depending upon the fluids by which the machines are operated and in types thereof.
1. With fluids by which the machine is operated:
Liquid, and Gas.
2. In Types:
An axial flow type, a mixed-flow type, and a centrifugal type.
Now, a mixed-flow pump is used mainly or widely due to easiness in operation thereof, and it comprises a suction casing, a pump and a diffuser, in a sequence from upper stream to down stream thereof.
A blade (of an impeller) rotating within a casing of the pump is rotationally driven on a rotary shaft, thereby supplying energy to the liquid which is suctioned from the suction casing. The diffuser has a function of converting a portion of velocity (or kinetic) energy of the liquid into static pressure.
A typical characteristic curve between a head and a flow rate of the turbo machine including the mixed-flow pump, where the horizontal axis shows a parameter indicating the flow rate while the vertical axis a parameter indicating the head, is as follows. Namely, it is common that the head falls down in the reverse relation to an increase of the flow rate in a region of low flow rate, however it has a characteristic of uprising at the right-hand side following the increase of the flow rate, during the time when the flow rate lies within a certain specific region. However, when the flow rate rises up further exceeding over the right-hand uprising region of the characteristic curve, the head begins to fall down, again, following the increase in the flow rate.
In a case where the turbo machine is operated with the flow rate of such the characteristic curve of uprising at the right-hand side, a mass of the liquid vibrates by itself, i.e., generating a surging phenomenon. It is believed that such the characteristic curve of uprising at the right-hand side is caused by, though the recirculation comes out at an outer edge of the inlet of the impeller when the flow rate flowing through the turbo machine is low, since at that instance, a flow passage or a channel for the liquid flowing into the impeller is narrowed and thereby generating a swirl in the liquid flowing into the impeller due to the influence of the recirculation mentioned above.
Since the surging gives damages not only upon the turbo machine, but also upon conduits or pipes which are connected to an upper-stream side and a down-stream side thereof, ordinarily, it is inhibited to be practiced in a region of low flow rate. Further, there were already proposed the following methods for suppressing the surging, other than an improvement made in the shape (i.e., profile) of the blade, for the purpose of expanding or enlarging the operation region of the turbo machine.
1. Casing treatment:
Thin or narrow grooves or drains, being from 10% to 20% of a chordal length of the blade, are formed in a casing region where the impeller lies, so as to improve a stall margin. Namely, with the casing treatment which were already proposed, the grooves being sufficient in the depth are formed in an inner wall (i.e., flow surface) of the casing in the region where the blades lie, in an axial direction, in a peripheral direction, or in an oblique direction, alternatively, in a radial direction or an oblique direction, respectively.
2. Separator:
A separator is provided for dividing the recirculation flow occurring at the outer edge of the inlet of the impeller into a reverse flow portion and a forward flow portion (i.e., in a main flow direction), in the region of low flow rate, thereby prohibiting the expansion of the recirculation.
As an example of a separator which is applied into the turbo machine of the axial flow type, in particular, there are proposed a suction ring type, a blade separator type, and an air separator type.
In the suction ring type, the reverse flow is enclosed within an outside of the suction ring, and in the blade separator type is provided a fin between the casing and the ring. Further, with the air separator type, a front end or a tip of the moving wing (i.e., the blade) is opened so as to introduce the reverse flows into the outside of the casing, thereby prohibiting the swirl from being generated due to the reverse flows by means of the fin. Thus, it is more effective, comparing with the former two types mentioned above, however, it comes to be large-scaled in the devices thereof.
3. Active control:
This is to suppress the generation of the swirl due to the recirculation by injecting or spouting out the high pressure fluid from an outside into a spot where the recirculation occurs.
Furthermore, as an example of the conventional turbo machines, a mixed-flow pump will be described hereinafter. To a mixed-flow pump, it is required to show a head-flow rate characteristic curve (hereinafter, called by xe2x80x9chead curvexe2x80x9d) having no behavior uprising at the right-hand side for enabling a stable operation, in a case where the pump is operated over the whole flow range thereof. However, ordinarily in a pump, it is common that the characteristics, such as an efficiency representing performance of the pump, a stability of the head curve, a cavitation performance, and an axial motive power for closure, etc., are in reversed relationships to one another. Namely, if trying to improve one of those characteristics, the other one(s) is is decreased down, therefore there is a problem that it is difficult to obtain improvements in at least two or more characteristics at the same time. For example, with a pump in which consideration was made primarily onto the efficiency thereof, the head curve shows a remarkable behavior uprising at the right-hand side in a portion thereof, thereby it has a tendency to be unstable.
For obtaining a head curve continuously falling down at the right-hand side for enabling the stable operation, in the conventional arts, as is mentioned in the above, it is already known that the casing treatment or the separator is provided or treated therein. Such the structure is already described, for example in U.S. Pat. No. 4,212,585.
Also, other than those, there is proposed a turbo machine, in which are formed plural pieces of grooves on the flow surface of the casing, for connecting between an inlet side of the impeller and an area or region of the flow surface of the casing where the blades reside, thereby obtaining a head curve having no such the characteristic of uprising at the right-hand side while suppressing the recirculation in the inlet thereof.
However, in accordance with the casing treatment and the separators of the prior arts mentioned above, although it is possible to shift the characteristic curve between head and flow rate including the portion uprising at the right-hand side into the lower flow rate side as it is, so as to expand the stable operation region thereof, however it is impossible to remove or cancel such the characteristic or behavior uprising at the right-hand side. Further, the turbo machine is decreased down by approximately 1% in the efficiency thereof, if it rises up by an every 10% in the stall margin, in accordance with the casing treatment.
Also, in such the active control, since there is a necessity to obtain the high pressure fluid from the turbo machine itself or an outside thereof, the efficiency of the turbo machine is decreased down as a whole system thereof.
Further, with a turbo machine, in which the grooves are formed for connecting between the inlet side of the impeller and the flow surface of the casing where the blades thereof reside, the processing of the grooves is easy and has a less decrease in an efficiency thereof, and it is also possible to obtain the head curve without such the uprising at the right-hand side in the characteristic thereof. However, there is not taken a consideration into a possibility that a fluctuation is generated in pressure due to interference between the flow from the blades of the impeller and the grooves when the blades pass by the plural grooves formed on the flow surface of the casing, thereby increasing vibration and noises.
An object, in accordance with the present invention, is to provide a turbo machine having a head-flow rate characteristic, which is improved in that of uprising at the right-hand side thereof, and enabling to suppress the decrease down of the efficiency thereof and further to suppress the increase up in the vibration and noises thereof.
Another object, in accordance with the present invention, is to provide a turbo machine, having an improved head-flow rate characteristic with respect to the turbo machine having a closed impeller, and enabling to suppress the decrease down of the efficiency thereof and the increase up in the vibration and noises thereof.
First, according to the present invention, for accomplishing the above-mentioned object, there is provided a turbo machine comprising: a casing; an impeller having a plurality of blades and being positioned within said casing; a plurality of first grooves being formed on an inner flow surface of said casing for conducting between an inlet side of said impeller and an area of the inner flow surface of said casing where the blades of said impeller reside in; and a second groove being formed on the inner flow surface of said casing for connecting said plurality of first grooves in a circumferential direction of said casing.
According to the present invention, it is preferable that in the turbo machine as defined in the above, wherein said plurality of first grooves are formed to be equal or greater than 5 mm in width, so that a total width of said plurality of the first grooves comes to be about 30%-50% with respect to a length of an inner circumference of the inner flow surface of said casing where the blades of said impeller reside in, and to be equal or greater than 2 mm in depth, so that it comes to be about 0.5%-1.6% with respect to a diameter of the inner flow surface of said casing where the blades of said impeller reside in.
Further, according to the present invention, it is preferable that in turbo machine as defined in the above, wherein said second groove is formed on the inner flow surface of said casing where the blades of said impeller reside in. And, also it is preferable that in turbo machine as defined in the above, wherein said second grooves are formed to be equal or shallower than said first grooves in depth thereof.
Further, according to the present invention, it is preferable that in turbo machine as defined in the above, wherein said second groove is formed from terminal ends of said first grooves at a down-stream side of said turbo machine, on the inner flow surface of said casing, up to the area where the blades of said impeller reside in, or up to the inlet side of said impeller.
Second, according to the present invention, there is provided a turbo machine comprising: a casing; an impeller having a plurality of blades and being positioned within said casing; and a plurality of grooves in a direction of pressure gradient of fluid, being formed on an inner flow surface of said casing, for communicating between an inlet side of said impeller and an area of the inner flow surface of said casing where the blades of said impeller reside in, wherein said grooves are formed in the direction of gradient in pressure of fluid so that they are inclined into a direction of rotation of said impeller, toward from a vicinity of an inlet portion of the impeller to a down-stream side of said turbo machine.
Third, according to the present invention, there is provided a turbo machine comprising: a casing; an impeller having a plurality of blades and being positioned within said casing; a plurality of first grooves in a direction of gradient in pressure of fluid, being formed on an inner flow surface of said casing at an inlet side of said impeller, over an inner circumference thereof; a second groove being formed on the inner surface of said casing, within an area where the blades of said impeller reside in, directing in a circumferential direction thereof; and a flow passage for connecting between said first grooves and said second groove.
Further, according to the present invention, in the turbo machine as defined in the above, wherein said flow passage is constructed with a groove, a bore, a conduit or a tube, etc., being formed bypassing the inner surface of said casing.
Fourth, according to the present invention, there is provided a turbo machine comprising: a casing; an impeller having a plurality of blades and being positioned within said casing; a plurality of first grooves in a direction of gradient in pressure of fluid, being formed on an inner surface of said casing at an inlet side of said impeller, over an inner circumference thereof; a second groove being formed on the inner surface of said casing within an area where the blades of said impeller reside in, directing in a circumferential direction thereof; and a third groove being formed on the inner surface of said casing in a vicinity of a front edge of the blades of said impeller, directing in the circumferential direction thereof; and a flow passage for connecting between said second groove and said third groove, wherein said flow passage is formed on a line extending from said first groove, bypassing the inner surface of said casing, so as to be communicated with said first groove through said third groove.
Fifth, according to the present invention, there is provided a turbo machine comprising: a casing; an impeller having a plurality of blades and being positioned within said casing; a plurality of grooves in a direction of gradient in pressure of fluid, being formed on an inner flow surface of said casing over an inner circumference thereof, for communicating between an inlet side of said impeller and an area of the inner flow surface of said casing where the blades of said impeller reside in; and movable members provided within said grooves in the direction of gradient in pressure of fluid, being movable in a radial direction of said casing so as to change depth of said grooves.
Sixth, according to the present invention, there is provided a turbo machine comprising: a closed-type impeller having a plurality of blades and a shroud thereabouts; a casing having an inner flow wall and receiving said impeller therein, wherein said impeller is formed into an open-type having no shroud thereabouts in vicinity of an inlet of said impeller; and a plurality of first grooves in a direction of gradient in pressure, being formed on an inner flow wall of said casing, opposing to a portion of said impeller having no shroud thereabouts in vicinity of the inlet thereof, over an inner circumference thereof, wherein a starting end of said first grooves at an inlet side is positioned at an upper flow side than a tip inlet side of said impeller, while a terminal end of said first grooves is positioned at a lower flow side than the tip inlet side of said impeller; and further comprising: a second groove for connecting said plurality of the first grooves in the circumferential direction of said casing, being formed on the inner flow wall of said casing, opposing to the portion of said impeller having no shroud thereabouts in vicinity of the inlet thereof.
Seventh, according to the present invention, there is provided a turbo machine comprising: an impeller; a casing receiving said impeller therein; a plurality of first grooves in a direction of gradient in pressure of fluid, being formed on an inner flow surface of said casing, opposing to an outer peripheral portion of blades of said impeller at an inlet side thereof, for connecting between an area where recirculation occurs at the inlet side of said impeller when flow rate is low and an area on the inner flow surface of said casing where tips of the blades of said impeller reside in, wherein terminals of said first grooves at a down-stream side of the turbo machine are positioned so that fluid of pressure can be taken out for suppressing a generation of the recirculation within a main flow, in inlets of said first grooves at an upper-stream side of the turbo machine; and a second groove being formed on the inner flow surface of said casing in a vicinity of the inlet of said impeller, for connecting said plurality of first grooves in a circumferential direction thereof, wherein portions of said casing where said first and second grooves are provided are formed as a body being separated from other portion of said casing.
According to the present invention, with the provision of the second groove(s), being formed in the area of said grooves where the impeller blades reside in, to be shallower, equal to or deeper than the first grooves in the depth, for making a portion of the first grooves continuous in the circumferential direction, the fluctuation in pressure, being caused due to the interference between the grooves and the flow from the impeller when the impeller blades pass by the grooves in the direction of gradient in pressure, is reduced or mitigated, thereby it is possible to suppress generation of the vibration and/or noises caused by the fluctuation in pressure.
Further, with forming the grooves in the direction of gradient in pressure (i.e., the first grooves), being inclined into the direction of rotation of said impeller (i.e., being wound into a reverse direction of curving of the impeller blades), it is also possible to reduced or mitigated the interference between the flow from the impeller and the grooves.
Further, the same effect can be obtained by forming the first grooves in the direction of gradient in pressure up to the inlet of the impeller, but constructing them not to overlap the second grooves in the circumferential direction, so that the grooves in the circumferential direction and the grooves in the direction of gradient in pressure are communicated with each other, thereby to take out the fluid of pressure for suppressing a generation of the recirculation within the main flow at the inlet of the impeller. Those two kinds of grooves mentioned above are preferable to be connected through the flow passages, being formed on the outer periphery of the casing escaping from the inner flow surface thereof where the main flow flows through. In this manner, it is possible to provide no such the grooves in the direction of gradient in pressure within the area on the inner flow surface of the casing where the impeller blades reside in, thereby enabling to reduce or mitigate the interference between the flow from the impeller and the grooves. The flow passages for connecting between the first grooves and the second grooves are preferably to be formed on the lines elongating from the first grooves, so that the fluid in the reverse direction against the main flow flows into the inlet side of the impeller blades.
Other features, objects and/or advantages obtained according to the present invention, will be apparent from the following explanation which will be made by referring to accompanying drawings.